Alley: ‘We Have High Confidence That Warming Will Shrink Greenland, By Enough To Matter A Lot To Coastal Planners’

At a dinner I attended last night, glaciologist Jason Box explained why he believes Greenland’s disintegration is likely to keep outpacing Antarctica’s for the foreseeable future. He has a detailed explanation at his blog, Meltfactor, reposted below. See also Chris Mooney’s interview of Box here and “Greenland Ice Melt Up Nearly Five-Fold Since Mid-1990s” – JR.

Icy contenders weigh in

by Jason Box, Ph.D.

Dahl-Jensen et al. (2013)[i] suggest that the Greenland ice sheet was more stable than previously thought[ii], enduring ~6k years of temperatures 5-8 C above the most recent 1000 years during the Eemian interglacial 118-126k years before present, its loss at the time contributing an estimated 2 m (6.6 ft) of global sea level compared to a total of 4-8 m (13-26 ft)[iii], implying Antarctica was and will become the dominant source of sea level change. Consequently, environmental journalist Andrew Revkin writes: “The dramatic surface melting [in Greenland], while important to track and understand has little policy significance.”

Given the non-trivial complexity of the issue and that Greenland has been contributing more than 2:1 that of Antarctica to global sea level in the recent 19 years (1992-2010)[iv], let’s not consider Greenland of neglible policy relevance until that ratio is 1:1 if not reversed, say, 0.5:1. Greenland, currently the leading contender with surface melting dominating its mass budget[v], the positive feedback with surface melting and ice reflectivity doubling Greenland’s surface melt since year 2000[vi]. Professor Richard Alley weighs in again: “We have high confidence that warming will shrink Greenland, by enough to matter a lot to coastal planners.”

That’s not to say that Antarctica couldn’t take over from Greenland the position of number 1 global sea level contributor in the foreseeable future. Nor should one be surprised if it did, given that Antarctica contains a factor of 10 more ice than Greenland[vii],[viii]. And it is probable that the planetary energy imbalance[ix] caused by elevated greenhouse gasses, expressed primarily through massive oceanic heat uptake[x], is delivering enough erosive power to destabilize the 3.3 m of sea level[xi] in the marine-based West Antarctic ice sheet. Yet, for today, consider also that climate change if increasing Antarctic precipitation a few percent can tip its mass balance toward the positive, lessening its sea level contribution[xii] even while its glaciers retreat.

Irrespective of sea level forcing, through its ice mass budget Greenland plays an important role to North Atlantic climate through ocean thermohaline circulation, even being suggested as the Achilles heel of the global climate system[xiii]. I wouldn’t tell our European friends Greenland’s hardly policy-relevant when climate change offers higher amplitude extremes in precipitation if not also temperature, as North Atlantic climate shifts in partial response to changes in neighboring Greenland.

Key differences between the modern Anthropocene and the Eemian interglacial suggest anthropogenic climate change may drive a different cryosphere response than during the Eemian…

Today, greenhouse gas concentrations are rising beyond 120% to 250% of peak Eemian values[xiv],[xv], driving today’s global warming and the aformentioned ocean heat content uptake that contrasts from the Eemian when warming was driven by northern latitudes receiving 30-50 Watts per sq. meter more solar energy, a more regionally-forced climate change. Anthropocene climate is forced an estimated 4/5 by by elevated greenhouse gasses and black carbon aerosols[xvi], the latter rising recently in significance after being more completely bounded[xvii]. Anthropogenic warming is clearly overwhelming the modern orbital cooling[xviii] and the decrease in solar output since the late 1970s[xix].

Because the Greenland ice sheet surface undergoes much more seasonal melting than the surface of the Antarctic ice sheet, in Greenland decanting a factor of 2 increase of meltwater runoff annually since 2000[xx], anthropogenic sources of light absorbing impurities provide a mechanism to multiply the cryospheric albedo feedback in ways presumably not occurring during the Eemian. Today, the combination of a.) land clearing by humans using fire, b.) industrial soot from fossil fuel combustion, and perhaps c.) larger fires the a legacy of fire suppression are in contrast to Eemian wildfire, that (as far as we know) did not include human factors. All me to here plug Dark Snow Project[xxi] that is currently soliciting donations to crowdfund a field and laboratory campaign designed to assess the impact of increasing wildfire on darkening the Greenland ice sheet.

Richard Alley: “While Antarctica is relatively unknown, Greenland is relatively known and therefore useful to guide policy even if the ice sheet becomes second most important to sea level, and to provide guidance to Antarctic colleagues [in surface melt studies]”

In the end, what matters to our concerns about the rate of sea level rise is the sum total volume change of all land ice. As long as glaciers and ice caps (GICs) (excluding the ice sheets) remain significant contenders (GICs lost mass at a rate of 148 ± 30 Gt per year from January 2003 to December 2010)[xxii], Antarctica lost 40% less during this period than GICs, and Greenland lost more than the two combined, we should stay focused on understanding the dynamics of all crysopheric systems in relation to the serious perturbation imposed by human activity. The Eemian has its own limits of utility in informing humanity of the trajectory we’re on.

18 Responses to Alley: ‘We Have High Confidence That Warming Will Shrink Greenland, By Enough To Matter A Lot To Coastal Planners’

NASA climate scientist James Hansen recently published an article on his web site that discusses Greenland and Antarctic ice sheet mass loss and potential sea level rise this century. In the article (which is not a peer-reviewed paper), Dr. Hansen reviews measurements of Greenland and Antarctic ice sheet loss and questions whether the mass loss is following a linear trend (like the IPCC assumes) or whether it is actually following an exponential trend. While a few more years of data are needed to confirm which trend is correct, the ice mass loss could conceivably be following an exponential trend (see Figure in link):http://www.columbia.edu/~jeh1/mailings/2012/20121226_GreenlandIceSheetUpdate.pdf

While the ice loss from Greenland and Antarctica currently only contribute about 1 mm to sea level rise each year, if it is following an exponential trend — in other words, if the mass loss doubles every certain amount of time — then the contribution to sea level rise could grow very rapidly. In the figure, a “doubling time” is plotted for 10 years (in green) and 5 years (in red). A straight-line linear trend is plotted as a black dashed line and the measured data is shown in blue. If the measured ice mass loss over the next few years continues its steep decline, then the process is likely exponential and sea level will rise rapidly this century. How rapidly? If the 10-year doubling time is correct, sea levels would increase 1m (3 feet) by around 2067. If the doubling time is instead 5 years, sea levels would increase by 1m (3 feet) by around 2045, just over 3 decades from now.

A process that doubles every 5 years experiences 10 doublings in 50 years. 10 doublings is 2x2x2x2x2x2x2x2x2x2=1024. In other words, if there is enough ice loss to cause sea levels to rise 1 millimeter/year before the 10 doublings, after the 10 doublings there will be enough ice loss to cause 1 meter/year (3 feet/year) of sea level rise. Plus you need to count the ice loss (and sea level rise) from the previous years, so things add up very quickly. In the 5-year doubling example, after 10 years the yearly rise is only 4mm (0.15 inches) and the cumulative rise is 23mm (1 inch). After 20 years, the yearly rise is 16mm (0.6 inches) and the cumulative rise is 116mm (4.5 inches). After 30 years, the yearly rise is 64mm (2.5 inches) and the cumulative rise is 0.5m (1.5 feet). In year 35, the yearly rise is 128mm (5 inches) and the cumulative rise is 1m (3 feet). Processes that have doublings (exponential trends) have a tendency to sneak up on you. When it comes to climate change, exponentials are not your friend.

Of course, if the exponential trend continues, sea levels will rise even more later this century and it would be possible, under business-as-usual emissions scenarios, to see 5m (16 feet) of sea level rise by the end of this century. Dr. Hansen thinks there may be a mechanism that will slow the melting when sea level rise reaches meter scale: the ice falling off Greenland and Antarctica will cool the surrounding oceans and that will slow the melting! As Dr. Hansen points out, this will be of little comfort for humanity since the regional cooling will increase the temperature gradient between the tropics and the poles and that will drive powerful cyclonic storms (Hansen’s “Storms of My Grandchildren”).

The chart alone is pretty clear. Greenland is accelerating. It’s probably linked to the Arctic Ocean’s absorption of heat, and the general explosion in summer temperatures on nearby land masses. Also, Antarctica is naturally colder and completely snow-covered, so that a 5 or 10 degree (F) rise in temperature doesn’t affect Antarctic melting that much. The albedo of Antarctica isn’t changing yet.

Surface melting of new pack ice causes albedo changes. Is this also true of Greenland’s ice sheet? Does a small melt pond on the ice sheet’s surface collect heat from sunlight?

Revkin’s “we don’t really need to do much or pay attention” message is one of the most irresponsible / destructive vectors in the media considering the eyes he gets…he’ll go right up there on the wall of infamy of the future with Watts, the Koch’s, Tillerson, Inhofe etc..

Some thing to note… This time round things are very different to the Eemian interglacial. It’s worse… Our forcing is much more and more rapid. Also there is the human stamp on the surface of things like forest clearing and fire burning Etc

I heard a woman, a Professor I believe, of some discipline, who has been engaged in planning for sea-level rise in this country, on the radio yesterday. I was somewhat inattentive, so I missed much, but the punch-line. She lamented that the mere mention of climate change had lately been expunged from all discussions on the problem, which the authorities (the new generation of hard Right extremist state regimes)preferred to ignore. Says it all, really.